This invention relates to electromotive motor structures and more particularly to improvements therein.
Piezoelectric motors or actuators of the type wherein PZ discs or PZ tubes interact with steel rods or tubes for the purpose of converting electrical signals into linear motion have a number of practical disadvantages. The fit of a disc with a tube or cylinder is subject to very close machining tolerances. The effect of differential thermal expansion and temperature differentials between the cylinder and the PZ material with which it interacts limit the ambient temperatures over which the unit may be operated to a narrow range. The PZ material will scrub heavily against the outer housing and thus will rapidly deteriorate.
Electromechanical actuators employing magnetic elements in the form of solenoids are unable to respond to proportionate signals and are either "full travel" or zero travel devices. If their programmed displacement is resisted, current in the coil windings increases and there is a danger of overheating with consequent coil failures.
Electromechanical actuators of the magnetic "torque motor" pattern can respond proportionately but their force capability is greatly limited and their displacement is heavily influenced by applied load. Electrorestrictive actuators can respond to proportionate signals and develop high force, but their displacement is very small and may be coupled only with the greatest difficulty and close tolerance machining.
PZ actuators have high force capability, proportional displacements, rapid response and high stiffness (insensitivity to applied load) but their small displacement usually demands some form of mechanical or hydraulic motion amplifier.